1 Slip and fall accidents are a major and growing source of occupational injuries. Shoes that are heavily worn 2 have reduced coefficient of friction (COF) and are associated with increased slipping risk. The mechanism 3 causing this loss of friction is that worn tread can no longer channel fluids from beneath the shoe, which causes 4 the fluid to become pressurized, the COF to decrease and the slip risk to increase. Key knowledge gaps exist 5 regarding the factors that contribute to shoe wear rate and the wear thresholds at which COF begins to 6 decrease. This gap inhibits selection of wear-resistant shoes and programs that replace shoes before they 7 become too worn. The overall objective of this R01 study is to fill this gap by identifying the underlying 8 causes to shoe wear and identifying the tread thresholds where shoes become unsafe. The proposed research 9 will accomplish this goal with: 1) experiments that identify the factors that contribute to wear rate (Aim 1) and 10 replacement thresholds for worn shoes (Aim 2); 2) a computational model that predicts wear rate and the life 11 expectancy of shoes (Aim 3); 3) a validation of Aims 1 and 3 based on tracking wear in occupational settings 12 (Aim 4); and 4) a validation of Aim 2 based on unexpected slips of participants donning naturally worn shoes 13 (Aim 5). To accomplish Aims 1 and 2, a shoe wear tester will reproduce the kinetics of stepping repeatedly to 14 accelerate the wear of the shoe tread. For Aim 1, the effects of shoe material and tread design on tread wear 15 rate will be quantified. For Aim 2, the impact of wear on COF and under-shoe fluid pressures will be 16 determined and tread thresholds where fluid pressures start to significantly increase will be identified. The 17 impact of fluid pressures on COF will be tested. For Aim 3, an iterative FEA model will be developed that 18 calculates wear based on the contact pressures and then updates the shoe geometry based on the calculated 19 wear. For Aim 4, two cohorts of twenty participants (one from Nabors Industries and one cohort from general 20 industry) will wear two different shoe designs. Shoe wear and number of steps will be tracked to validate the 21 degree to which the wear rates observed in the experiments (Aim 1) and the model (Aim 3) reflect actual wear 22 experienced in industry. For Aim 5, sixty individuals will be unexpectedly slipped while wearing naturally 23 worn shoes. This aim will validate the effect of shoes worn beyond their replacement limits (determined in Aim 24 2) on slip risk. This proposal will meet NIOSH's Research to Practice (R2P) initiative by identifying the 25 factors that affect the life of shoes and their replacement limits, which will be translated to practice through 26 industry partners, publications and training programs. The outputs of this research will be new knowledge on 27 when worn shoes should be replaced, what factors influence wear, and a computational model of shoe wear. 28 The outcomes will be improved shoe design and replacement policies that lead to a reduction in slip and fall 29 accidents from worn shoes. This research will address NORA Strategic Goals for Manufacturing (Goal 2), 30 Wholesale and Retail Trade (Goal 2) and Oil and Gas Extraction (Goal 4.2).